The present invention relates to a porous-matrix optical biosensor. In particular, the present invention relates to an optical biosensor with porous matrix constituted by anodized porous alumina connected to a detector, preferably a photodiode, for detection of the signal. The present invention moreover relates to a biosensor having an optical detector integrated with a porous matrix other than porous alumina, such as for example porous silicon.
A biosensor is a device capable of detecting a chemical or biochemical variable (analyte) by means of a biological component (biomediator), which, being immobilized on a matrix/substrate, functions as interface with a transducer. The transducer, which is constituted by the sensitized matrix and by a detector, is capable of transforming the chemico-physical signal deriving from the interaction between the biomediator and the analyte into a measurable physical (i.e., electrical) signal, which depends upon the variable analysed. The detector is able to measure the physical signal both in purely qualitative terms and in quantitative terms.
An optical biosensor is a device capable of measuring the luminescence—whether chemiluminescence or bioluminescence—emitted during the interaction between the biomediator and its corresponding biological variable. Said interaction entails, in fact, occurrence of a chemical reaction which brings about the passage of one of the species involved in the reaction into an electronically excited state. Decay of said species from the excited state to the fundamental state brings about emission of photons (hν), the measurement of which supplies an indication not only of the presence but also of the amount of the analyte being measured.
The essential characteristics of biosensors are the sensitivity and the selectivity that the biological component is able to provide, in conjunction with the simplicity of use and the versatility that derives from the method of transduction chosen, which is usually compatible with specifications of low-cost miniaturizability.
The biomediators or biological systems used may be enzymes (e.g., luciferase), antibodies, biological membranes, bacteria of a wild strain or genetically modified bacteria (e.g., natural or recombinant bioluminescent bacteria), cells, animal or vegetable tissues; these interact directly or indirectly with the analyte to be determined and are responsible for the specificity of the sensor. The biomediator interacting with the analyte brings about a variation in one or more chemico-physical parameters of the species involved, giving, for example, rise to a chemiluminescent or bioluminescent reaction with corresponding emission of photons (hν).
The substrates used for immobilization of the biomediator can be constituted by various materials. Amongst the currently used ones there can mentioned silica gel, agarose, polymeric compounds such as, for example, polystyrene or polyacrylates, natural fibres such as silk, or else glass (micro)spheres.
The areas of application of biosensors are very wide and range from the medico-diagnostic sector to the environmental and foodstuff sectors.
In the foodstuff sector, biosensors can be used for determining chemical substances that may function as indicators, for example, of the microbial pollution present in a foodstuff or of the deterioration of the latter, for example caused by processes of oxidation. It is moreover possible to detect traces of contaminating chemical compounds, toxins, or else additives, preservatives, etc.
Also the applications in the environmental sector are extremely numerous for determining the presence of pesticides, hydrocarbons, and toxic gases. In many cases, on account of the need to detect levels of concentration that fall below the range of detection of the biosensor, the latter has been coupled, in the case of electrical transduction, to electronic amplifiers.